This invention relates to the field of integrated circuit electronic networks providing selectable degrees of signal phase shift at microwave operating frequencies.
Phased array radar antennas and other microwave apparatus have need of digitally selectable phase delaying networks which are both low in fabrication cost and of the smallest possible physical size. For operating frequencies above ten gigahertz the use of distributed components in these phase shifting networks has become an accepted design practice in the microwave art. For frequencies below ten gigahertz, however, distributed component phase shifting components such as quarter wavelength microstrip delay lines become prohibitively long in physical size for implementation on an integrated circuit chip. In addition to the difficulty of containing these large phase shifting network components in an electronic apparatus--an apparatus which is almost always limited in physical size--the cost of fabricating these unduly large sized networks is found to be directly related to the physical size of the integrated circuit chip used to contain the network so that the large size in itself promotes undesirable apparatus cost.
The prior patent art includes several examples of previous phase shifting network practices. Included in these prior patents is the U.S. Pat. No. 4,471,329 of E. C. d'Oro which concerns a microstrip waveguide structure; the U.S. Pat. No. 4,471,330 of Naster et al which shows a conventional digital phase shifting bit that incorporates high frequency transmission lines; the U.S. Pat. No. 4,556,808 of Coats in which integrated lumped element pi-networks replace quarter wavelength transmission lines in a switching circuit arrangement; the U.S. Pat. No. 4,612,520 of Borie et al which describes a wideband 180 degree phase shifter bit that includes both transmission line segments and a pi-network; the U.S. Pat. No. 4,630,010 of Yarman which shows a low pass digital phase shifter for use at extra high frequencies; and the U.S. Pat. No. 4,652,883 of Andricos which concerns a signal phase shifter for use in a phased array radar system. None of these prior patents, however, achieves the advantages of the lumped element digital phase shifter bit of the present invention.